In 2008, the Water Resources Institute in Washington D.C., identified excess nutrients in water as one of the leading causes of water degradation, and reported over 415 areas worldwide experiencing the devastating economic and environmental effects of eutrophication (algal bloom) and hypoxia (oxygen dissolved depletion). Recent surveys in United States and Europe found that a staggering 78 percent of the assessed continental U.S. coastal area and approximately 65 percent of Europe's Atlantic coast exhibit symptoms of eutrophication. Furthermore, trends in agricultural practices, energy use, and population growth indicate that coastal eutrophication will be an ever growing problem.
To combat hypoxia it is essential to reduce nutrients from land-based wastewater reaching rivers in runoff. This is effectively achieved by an adequate treatment of sewage and by reducing agricultural fertilizers reaching surface waters. It is estimated that 25% of all water body impairments are due to the effects associated with the excess of nutrients in water (oxygen depletion, algal growth, biological extinction). To palliate these effects municipalities have begun looking beyond conventional treatment technologies and have lowered effluent discharge limits for nitrogen and phosphorous compounds. These advanced technologies involve new bioreactors and/or biological processes.
About one-third of the influent phosphorous in wastewater treatment plants (WWTP) is removed by both the settling of the insoluble fraction, and by cellular growth which occurs in both primary and secondary treatments. Typical heterotrophic bacteria present in secondary treatment use phosphorous for cellular growth to make up 2.5% of their weight. The complete removal of nutrients occurs after the secondary treatment. That is, after the elimination of carbon and ammonia pollutants. These processes are followed by both denitrification to eliminate the nitrates, and by phosphorous removal. Currently, phosphorous removal is primarily done by the addition of coagulants and flocculants. Because these chemicals create much sludge and are expensive, biological phosphorous removal is becoming the preferred option. In view of the foregoing, it would be desirable to develop a more efficient and cost effective method for nutrient removal.